This invention relates to fuel controls for gas turbine types of power plant and particularly to an improved throttle valve, its servo system and its multiplication linkage system.
This invention constitutes an improvement over the type of fuel control exemplified by, for example, the JFC-25, JFC-60 manufactured by the Hamilton Standard Division of United Aircraft Corporation and the type disclosed in U.S. Pat. No. 2,822,666 granted to S. G. Best on Feb. 11, 1958 and assigned to the same assignee. As is well known the throttle valve utilized in the above mentioned controls are all of the type that is servoed and it together with its associated mechanism and the multiplying linkage are considered relatively large and consequently heavy.
Conventionally, the throttle valve, which serves to meter fuel flow to the burner section of the power plant, is positioned in response to the multiplicand of W.sub.f /P.sub.3 .times. P.sub.3 where W.sub.f equals fuel flow in pounds per hour and P.sub.3 is compressor discharge pressure in pounds per square inch. Also, conventionally the W.sub.f /P.sub.3 signal is scheduled and is manifested in a linkage position relative to a fulcrumed lever and P.sub.3 is manifested as a force applied to that linkage so that the moment arm on the fulcrumed lever is manifested as the input to the servo system for positioning the throttle valve. Essentially, the fulcrumed lever establishes the curtain area of the jet nozzle which, in turn, controls flow and pressure to the servo piston for positioning the throttle valve. A force balance feedback system nulls the servo in a conventional manner.
I have found that I can reduce the size of the hydraulic piston of the servo system, hence the size of the throttle valve, which in turn, results in a reduction of size in the overall multiplication, feedback and servo systems, without sacrificing accuracy by including means, judiciously located, to rotate the piston, throttle valve combination. While, it is known that pilot valves, for example, are rotated in order to overcome stiction (static friction) problems, such never manifested a reduction in size and weight. Because of the problems inherent with rotating valves, it was understood by those skilled in the art that the inclusion of the rotating mechanism would not result in a weight reduction, but in fact, would result in a weight increase. To the contrary, I was able to not only reduce the overall weight significantly, but in fact, increased the accuracy of the metering system.
It is conventional in the heretofore known fuel controls of the type that utilizes a flapper type of servo control valve to include compensating means to compensate for the change in impact forces on the fulcrumed lever resulting from the flow egressing from the flapper nozzle at different curtain areas because of the changes in pressure of the fluid in the nozzle. This hardware such as bellows, levers, additional flow lines, etc. to achieve this compensation is completely eliminated by virtue of this invention.
According to this invention the maximum fuel flow limiter which serves to limit the maximum amount of fuel that the fuel control can meter to the engine changes the feedback system from a force balance to a position feedback and utilizes the flapper and servo system directly requiring a smaller load in comparison to the prior art system and realizing a reduction in size and weight of these elements.
Additionally, by virtue of this invention I found that I could significantly improve the response time from the time a command signal was initiated until the output was manifested. In the case of weight reduction, it was found that the portion of the fuel control attributable to the metering and multiplication system at least a 30% savings was realized and in the case of time responsiveness an improvement of at least 50% was attained.